1. Field of the Invention
This invention relates generally to pulse width discriminators and particularly to a discriminator capable of handling multiplexed input signals.
2. Description of the Prior Art
Many pulse width discriminators have been described in the prior art. Among these is the patent to Smith, U.S. Pat. No. 3,790,881. It discloses a pulse width selector or discriminator. The apparatus accepts or rejects pulses on the basis of pulse duration. The pulses are clocked into a shift register and the counter is checked at the end of the pulse to determine whether the pulse duration is within predetermined limits. Accordingly, this device is entirely digital. The same applies to the patent to Gravett, U.S. Pat. No. 3,978,445. Here a digital counter is used in counting a clock gated by the signal. A similar digital pulse width decoder is disclosed in the patent to Odom, U.S. Pat. No. 3,948,199.
Another group of patents discloses charge coupled devices (CCD). For example, the patent to Puckette et al., U.S. Pat. No. 3,787,852, discloses a plurality of bucket brigade delay line circuits or charge coupled devices. They are used in parallel in a radar receiver signal path. Portions of the received signal are clocked into the bucket brigade delay line circuit serially. Accordingly, each radar pulse repetition period is divided into a plurality of sub-periods, and a selected sub-period is stored in each bucket brigade delay line circuit. These may then be processed by moving target indicator (MTI) techniques.
The patent to Cheek, Jr., et al., U.S. Pat. No. 3,947,698, also utilizes a charge coupled device which is utilized as a shift register and performs multiplexing functions only. However, the patent does not direct itself to pulse width discrimination.
The patent to Leach, Jr., U.S. Pat. No. 4,028,671, discloses a CCD recirculating memory to recirculate data. There is no disclosure how this could be used for pulse width discrimination.
Finally, the patent to Mattern, U.S. Pat. No. 4,063,200, discloses a multiplexed filter bank having a digital-to-analog multiplier for weighting sampled input signals. The multiplexed filter bank forms a rather general multiplexed recursive filter.